Release 1.2.0

• Added: via_midpoints argument to krotov.conversions.discretize
  function
• Changed: Controls and update shapes are now discretized in a way
  that ensures numerical stability (#74, thanks to @zachmanson)
• Changed: Replaced uniseg dependency with grapheme (#76)

Note: due to the changes in the time discretization of the controls and
update shapes, this version will generally not reproduce optimization
results from previous versions to machine precision.